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It is believed that many inexperienced people do not know what to do about how to read student card data in Android NFC development. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

Use hardware: Google Nexus S, Peking University student card.

Mobile operating system: Android ICS 4.04.

During the development, the author downloaded the NFC TagInfo software from Google Play Store for comparative study. So we can use any card that can be correctly identified by TagInfo software for testing.

In Android NFC applications, Android mobile phones are usually used as the initiator of communication, that is, as the reader and writer of various NFC cards. Android's support for NFC is mainly in the android.nfc and android.nfc.tech packages.

The main classes in the android.nfc package are as follows:

NfcManager can be used to manage all the NFCAdapter indicated in Android devices, but since most Android devices support only one NFCAdapter, getDefaultAapater is usually called directly to get the Adapter in the phone.

NfcAdapter is equivalent to a NFC adapter, similar to a computer with a network adapter to surf the Internet, and a mobile phone with a NfcAdapter to initiate NFC communications.

NDEF: NFC Data Exchange Format, or NFC data interchange format.

The data format defined by NdefMessage and NdefRecord NDEF for NFC forum.

Tag represents a passive Tag object, which can represent a label, card, etc. When the Android device detects a Tag, it creates a Tag object, places it in the Intent object, and sends it to the appropriate Activity.

Android.nfc.tech defines classes that can read and write to Tag. These classes can be divided into different classes according to the type of technology they use, such as NfcA, NfcB, NfcF, and MifareClassic. Among them, MifareClassic is more common.

In this example, the author uses Peking University student card for data reading test, and the TAG type of student card is MifareClassic.

AndroidManifest.xml:

Res/xml/nfc_tech_filter.xml:

Android.nfc.tech.MifareClassic

When the phone turns on NFC and detects a TAG, the TAG distribution system automatically creates an intent that encapsulates the NFC TAG information. If more than one application can handle the intent, the phone will pop up a box for the user to select the Activity that handles the TAG. The TAG distribution system defines intent in 3. In order of priority, they are as follows:

NDEF_DISCOVERED, TECH_DISCOVERED, TAG_DISCOVERED

When the Android device detects an NFC Tag approach, it sends an Intent with a NFC message to the corresponding Activity according to the order stated by the Action.

The Action type of the intent-filter we use here is TECH_DISCOVERED so that we can handle all TAG of type ACTION_TECH_DISCOVERED and the technology used is the type defined in the nfc_tech_filter.xml file.

For more information, please see the official documentation. The following figure shows the matching process of enabling Activity when the phone detects a TAG.

Res/layout/main.xml:

The layout of the Activity is defined: only one TextView with a scroll bar is used to display information read from the TAG.

Res/values/strings.xml:

NFC test scan in progress.

Src/org/reno/Beam.java:

Package org.reno; import android.app.Activity; import android.content.Intent; import android.nfc.NfcAdapter; import android.nfc.Tag; import android.nfc.tech.MifareClassic; import android.os.Bundle; import android.widget.TextView; public class Beam extends Activity {NfcAdapter nfcAdapter; TextView promt; @ Override public void onCreate (Bundle savedInstanceState) {super.onCreate (savedInstanceState); setContentView (R.layout.main) Promt = (TextView) findViewById (R.id.promt); / / get the default NFC controller nfcAdapter = NfcAdapter.getDefaultAdapter (this); if (nfcAdapter = = null) {promt.setText ("device does not support NFC!") ; finish (); return;} if (! nfcAdapter.isEnabled ()) {promt.setText ("Please enable the NFC feature in the system setup first!") ; finish (); return;}} @ Override protected void onResume () {super.onResume () / / get whether ACTION_TECH_DISCOVERED triggers if (NfcAdapter.ACTION_TECH_DISCOVERED.equals (getIntent (). GetAction () {/ / process the intent processIntent (getIntent ()) }} / / character sequence converted to hexadecimal string private String bytesToHexString (byte [] src) {StringBuilder stringBuilder = new StringBuilder ("0x"); if (src = = null | | src.length > > 4) & 0x0F, 16); buffer [1] = Character.forDigit (src [I] & 0x0F, 16); System.out.println (buffer) StringBuilder.append (buffer);} return stringBuilder.toString ();} / * Parses the NDEF Message from the intent and prints to the TextView * / private void processIntent (Intent intent) {/ / remove the TAG Tag tagFromIntent = intent.getParcelableExtra (NfcAdapter.EXTRA_TAG) encapsulated in intent For (String tech: tagFromIntent.getTechList ()) {System.out.println (tech);} boolean auth = false; / / read TAG MifareClassic mfc = MifareClassic.get (tagFromIntent); try {String metaInfo = ""; / / Enable Imax O operations to the tag from this TagTechnology object. Mfc.connect (); int type = mfc.getType (); / / get the type of TAG int sectorCount = mfc.getSectorCount (); / / get the number of sectors contained in TAG String typeS = ""; switch (type) {case MifareClassic.TYPE_CLASSIC: typeS = "TYPE_CLASSIC"; break Case MifareClassic.TYPE_PLUS: typeS = "TYPE_PLUS"; break; case MifareClassic.TYPE_PRO: typeS = "TYPE_PRO"; break; case MifareClassic.TYPE_UNKNOWN: typeS = "TYPE_UNKNOWN"; break } metaInfo + = "Card Type:" + typeS + "\ nTotal" + sectorCount + "Total sector\ nTotal" + mfc.getBlockCount () + "Block\ nStorage Space:" + mfc.getSize () + "B\ n"; for (int j = 0; j)

< sectorCount; j++) { //Authenticate a sector with key A. auth = mfc.authenticateSectorWithKeyA(j, MifareClassic.KEY_DEFAULT); int bCount; int bIndex; if (auth) { metaInfo += "Sector " + j + ":验证成功\n"; // 读取扇区中的块 bCount = mfc.getBlockCountInSector(j); bIndex = mfc.sectorToBlock(j); for (int i = 0; i < bCount; i++) { byte[] data = mfc.readBlock(bIndex); metaInfo += "Block " + bIndex + " : " + bytesToHexString(data) + "\n"; bIndex++; } } else { metaInfo += "Sector " + j + ":验证失败\n"; } } promt.setText(metaInfo); } catch (Exception e) { e.printStackTrace(); } } } 关于MifareClassic卡的背景介绍：数据分为16个区(Sector) ,每个区有4个块(Block) ，每个块可以存放16字节的数据。 每个区***一个块称为Trailer ，主要用来存放读写该区Block数据的Key ，可以有A，B两个Key，每个Key 长度为6个字节，缺省的Key值一般为全FF或是0. 由 MifareClassic.KEY_DEFAULT 定义。 因此读写Mifare Tag 首先需要有正确的Key值（起到保护的作用），如果鉴权成功，然后才可以读写该区数据。 执行效果：

After reading the above, have you mastered the method of how to read student card data in Android NFC development? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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